1. Field of the Invention
This invention relates to a method of and an apparatus for checking the wrapping state of a wrapped roll of a continuous sheet material which is rolled around a core tube and wrapped with wrapping sheet and the like.
2. Description of the Related Art
There have been known various wrapping materials and wrapping methods for wrapping a roll of sheet material. For example, in one of the known wrapping methods, a leader sheet is bonded to the leading end of the rolled sheet material and an end face cover is bonded to each side edge portion of the leader sheet. The leader sheet is rolled around the sheet roll to cover the side surface of the sheet roll and then the end face covers are folded along the end faces of the roll to cover the end faces and the free edge portion of each end face cover is tucked into the end portion of the core tube. Thereafter a bushing having an outer diameter slightly smaller than the inner diameter of the core tube is press-fitted into each end of the core tube over the tucked portion of the end face cover to fix the cover on the roll.
The wrapping material comprising such a leader sheet and such end face covers is employed, for instance, to wrap a roll of photosensitive material sheet such as photographic film. The wrapping material is so arranged that the outer edges of the bonded area of the leader sheet and the end face covers run along the side edges of the sheet roll and when the leader sheet is pulled, the end face covers are easily torn along the outer edges of the bonded area, whereby the wrapped roll is opened. When the outer edges of the bonded area are not correctly positioned along the side edges of the roll and are on the side surface of the roll, the force required to pull the leader sheet increases and in extreme cases, the end face covers cannot be torn along the outer edges of the bonded area and the leader sheet cannot be properly drawn out.
Further, when the end face covers are not sufficiently bonded to the leader sheet, or the bonded area is blemished, or folding of the end face covers is defective, light-shielding performance and/or water vapor barrier characteristics of the wrapped roll can deteriorate.
Further, when tucking of the end face covers into the core tube is defective, the bushings cannot be fit in the core tube with a sufficient force, which can result in poor light-shielding performance and/or water vapor barrier characteristics of the wrapped roll and/or bushings slipping off during transfer of the wrapped roll.
Especially when the rolled sheet material is photosensitive sheet, the performance of the sheet material deteriorates if the light-shielding performance and/or water vapor barrier characteristics of the wrapped roll are poor. For example, a roll of photosensitive sheet material wrapped in a dark room will be exposed to light as soon as it is transferred to a light room. Accordingly if a defect in wrapping state is found in a dark room, the roll must be rewrapped before transferring to a light room.
However, there has not been developed an apparatus for automatically checking the wrapping state of a wrapped roll and conventionally wrapping state has been visually checked. Such a method of checking wrapping state of the rolled sheet is disadvantageous in that it takes a large amount of labor to visually check a large number of rolls and reliability of the check is poor.